Buggy code:
public class JaspellTernarySearchTrie { protected final class TSTNode { protected static final int PARENT = 0 ; protected static final int LOKID = 1 ; protected static final int EQKID = 2 ; protected static final int HIKID = 3 ; protected Object data ; protected JaspellTernarySearchTrie . TSTNode [ ] relatives = new JaspellTernarySearchTrie . TSTNode [ 4 ] ; protected char splitchar ; protected TSTNode ( char splitchar , JaspellTernarySearchTrie . TSTNode parent ) { } } private static int compareCharsAlphabetically ( char cCompare2 , char cRef ) { } private int defaultNumReturnValues = - 1 ; private int matchAlmostDiff ; private JaspellTernarySearchTrie . TSTNode rootNode ; private final Locale locale ; public JaspellTernarySearchTrie ( ) { } public JaspellTernarySearchTrie ( Locale locale ) { } void setRoot ( JaspellTernarySearchTrie . TSTNode newRoot ) { } JaspellTernarySearchTrie . TSTNode getRoot ( ) { } public JaspellTernarySearchTrie ( File file ) throws IOException { } public JaspellTernarySearchTrie ( File file , boolean compression ) throws IOException { } private void deleteNode ( JaspellTernarySearchTrie . TSTNode nodeToDelete ) { } private JaspellTernarySearchTrie . TSTNode deleteNodeRecursion ( JaspellTernarySearchTrie . TSTNode currentNode ) { } public Object get ( CharSequence key ) { } public Float getAndIncrement ( String key ) { } protected String getKey ( JaspellTernarySearchTrie . TSTNode node ) { <START_BUG> StringBuffer getKeyBuffer = new StringBuffer ( ) ; <END_BUG> getKeyBuffer . setLength ( 0 ) ; getKeyBuffer . append ( ( "" + ( node . splitchar ) ) ) ; JaspellTernarySearchTrie . TSTNode currentNode ; JaspellTernarySearchTrie . TSTNode lastNode ; currentNode = node . relatives [ JaspellTernarySearchTrie . TSTNode . PARENT ] ; lastNode = node ; while ( currentNode != null ) { if ( ( currentNode . relatives [ JaspellTernarySearchTrie . TSTNode . EQKID ] ) == lastNode ) { getKeyBuffer . append ( ( "" + ( currentNode . splitchar ) ) ) ; } lastNode = currentNode ; currentNode = currentNode . relatives [ JaspellTernarySearchTrie . TSTNode . PARENT ] ; } getKeyBuffer . reverse ( ) ; return getKeyBuffer . toString ( ) ; } public JaspellTernarySearchTrie . TSTNode getNode ( CharSequence key ) { } protected JaspellTernarySearchTrie . TSTNode getNode ( CharSequence key , JaspellTernarySearchTrie . TSTNode startNode ) { } protected JaspellTernarySearchTrie . TSTNode getOrCreateNode ( CharSequence key ) throws IllegalArgumentException , NullPointerException { } public List < String > matchAlmost ( String key ) { } public List < String > matchAlmost ( CharSequence key , int numReturnValues ) { } private List < String > matchAlmostRecursion ( JaspellTernarySearchTrie . TSTNode currentNode , int charIndex , int d , CharSequence matchAlmostKey , int matchAlmostNumReturnValues , List < String > matchAlmostResult2 , boolean upTo ) { } public List < String > matchPrefix ( String prefix ) { } public List < String > matchPrefix ( CharSequence prefix , int numReturnValues ) { } public int numDataNodes ( ) { } protected int numDataNodes ( JaspellTernarySearchTrie . TSTNode startingNode ) { } public int numNodes ( ) { } protected int numNodes ( JaspellTernarySearchTrie . TSTNode startingNode ) { } public void put ( CharSequence key , Object value ) { } private int recursiveNodeCalculator ( JaspellTernarySearchTrie . TSTNode currentNode , boolean checkData , int numNodes2 ) { } public void remove ( String key ) { } public void setMatchAlmostDiff ( int diff ) { } public void setNumReturnValues ( int num ) { } protected List < String > sortKeys ( JaspellTernarySearchTrie . TSTNode startNode , int numReturnValues ) { } private List < String > sortKeysRecursion ( JaspellTernarySearchTrie . TSTNode currentNode , int sortKeysNumReturnValues , List < String > sortKeysResult2 ) { } }

Fix:
StringBuilder getKeyBuffer = new StringBuilder ( ) ;